The present invention relates to a thermal transfer recording medium, to an image forming method using the thermal transfer recording medium, and to an image-bearing article formed by the image forming method. In particular, the present invention relates to a method of forming an image based on an area gradation formed of dots, wherein a thermal head printer and a thermal transfer recording medium (thermal ink-transfer ribbon) having a thermal transfer recording layer containing a coloring pigment are employed to thermally transfer the thermal transfer recording layer, in a form of image based on an image data, onto an image-receiving sheet.
More specifically, this invention relates to a thermal transfer recording medium which is suited for use in forming a gradation color image based on area gradation which can be obtained by superimposing dots of multi-color thermal transfer recording layers comprising at least two kinds of color layer, to an image forming method using the thermal transfer recording medium, and to an image-bearing article formed by the image forming method.
With respect to the thermal transfer recording system for forming a gradation image by making use of a thermal head printer, two kinds of transfer systems are known up to date, i.e. a sublimation transferring system and a fusion transferring system.
According to the sublimation transferring system, a thermal transfer recording medium, which is formed of a substrate and a thermal transfer recording layer formed on the substrate and containing a sublimable dye (thermal transfer dye) and a resinous binder, is superimposed on an image-receiving sheet, and then, the sublimable dye in the thermal transfer recording layer is allowed to transfer, in conformity with the quantity of heat from a thermal head, to the image-receiving sheet, thereby forming a gradation image on the image-receiving sheet.
However, when an image is formed by making use of a sublimable dye (thermal transfer dye), the image thus formed is generally poor in durability, so that the application of the sublimation transferring system to the fields where excellency in heat resistance or light-resistance of printed image is demanded would be limited. Further, the thermal transfer recording medium to be employed in the sublimation transferring system is defective in that since the thermal recording sensitivity of the thermal transfer recording medium is poor as compared with the recording medium to be employed in the fusion transferring system, the thermal transfer recording medium is not suited for use as a high-speed recording material to be employed in a recording system employing a high-resolution thermal head which is expected to be actually employed in future for the miniaturization and lightening of a printer to be driven by a battery such as dry battery.
On the other hand, according to the fusion transferring system, a transfer sheet, which is formed of a substrate and a thermally fusible ink transfer layer formed on the substrate and containing a colorant such as dye or pigment and a binder such as wax is superimposed on an image-receiving sheet, and then, energy is applied to a heating device such as a thermal head in conformity with an image data so as to fusion-bond parts of the ink transfer layer to the image-receiving sheet, thereby forming an image. The image formed by way of the fusion transferring system is excellent in density and sharpness and is suited for use in recording a binary image such as letters and linear image. Further, the fusion transferring system enables forming a color image by superimposing a thermal ink-transfer sheet bearing yellow, magenta, cyan and black ink layers on an image-receiving sheet, aside from a low quality of image derived from a low suitability of gradation representation. Such a thermal ink-transfer sheet for forming a color image is disclosed in Japanese Patent Publication S63-65029.
However, in the case of the thermal ink-transfer sheet disclosed in this Japanese Patent Publication S63-65029, since a crystalline wax having a low melting point is employed as a binder for the ink layer, the blurring of ink tends to occur to thereby deteriorating the resolution of image. Additionally, the fixing strength of the image transferred is relatively weak, so that when an image portion is strongly rubbed with one""s fingers, the image portion may be vanished.
With a view to solve this problem, various methods have been proposed. For example, a heat sensitive transfer sheet bearing a heat sensitive ink layer comprising not less than 65% of amorphous polymer, a releasable material and a colorant is proposed in Japanese Patent Unexamined Publication S61-244592.
However, even in the case of the heat sensitive transfer sheet disclosed in this Japanese Patent Unexamined Publication S61-244592, since a crystalline wax is included in the ink layer, the fixing strength of the portion where a plurality of color images are superimposed is still insufficient.
An object of the present invention is to provide a thermal transfer recording medium which is capable of improving the resolution of images, suitability of gradation representation based on area gradation, the durability of images transferred, the sharp cutting property of the transfer recording layer, and the optical density of transferred image.
Another object of the present invention is to provide an image forming method using the aforementioned thermal transfer recording medium.
A further object of the present invention is to provide an image-bearing article formed by the aforementioned image forming method.
According to a first embodiment of the present invention, there is provided a thermal transfer recording medium comprising; a substrate; and multi-color thermal transfer recording layers, each of the multi-color thermal transfer recording layers being repeatedly formed for each color along the longitudinal direction of the substrate; wherein each of the multi-color thermal transfer recording layers contains a coloring pigment, an amorphous organic polymer and fine particles, and at least one of the multi-color thermal transfer recording layers is formed to have a larger thickness than the other of the multi-color thermal transfer recording layers.
Further, according to a first embodiment of the present invention, there is also provided a method of forming an image by means of a thermal head and by making use of the aforementioned thermal transfer recording medium, the method comprising a step of thermally transferring thermal transfer recording layers of the thermal transfer recording medium to an image-receiving member on a basis of image data to thereby form an image based on an area gradation; the image-receiving member being provided, on the image reception surface thereof, with a layer containing the same kind of amorphous organic polymer as the amorphous organic polymer included in the thermal transfer recording layers.
Still further, according to a first embodiment of the present invention, there is also provided a method of forming an image by means of a thermal head and by making use of a plurality of thermal transfer recording mediums of different colors, each of the thermal transfer recording mediums comprising a substrate and a single-color thermal transfer recording layer formed on the substrate and containing a coloring pigment, an amorphous organic polymer and fine particles, the method comprising a step of successively thermally transferring the single-color thermal transfer recording layers of the thermal transfer recording mediums for each color to an image-receiving member on a basis of image data to thereby form an image based on an area gradation, wherein the single-color thermal transfer recording layer of thermal transfer recording medium is formed to have a larger thickness than the single-color thermal transfer recording layer of the other thermal transfer recording medium.
Still further, according to a first embodiment of the present invention, there is also provided an image-bearing article comprising; an image carrier; and transferred multi-color image of dots formed on the image carrier through a successive thermal transferring using the aforementioned thermal transfer recording medium; wherein the dots of at least one color in the transferred multi-color image is formed to have a larger thickness than that of the dots of the other color in the transferred multi-color image.
According to a second embodiment of the present invention, there is provided a thermal transfer recording medium comprising; a substrate; and multi-color thermal transfer recording layers, each of the multi-color thermal transfer recording layers being repeatedly formed for each color along the longitudinal direction of the substrate; wherein each of the multi-color thermal transfer recording layers contains a coloring pigment, an amorphous organic polymer and fine particles, and each of the multi-color thermal transfer recording layers which are successively transferred, excluding the color thermal transfer recording layer to be transferred latest, is formed to have an average thickness of 0.6 xcexcm or less.
Further, according to a second embodiment of the present invention, there is provided a method of forming an image by means of a thermal head printer and by making use of the aforementioned transfer recording medium, the method comprising a step of thermally transferring thermal transfer recording layers of the thermal transfer recording medium to an image-receiving member on a basis of image data to thereby form an image based on an area gradation; the image-receiving member being provided, on the image reception surface thereof, with a layer containing the same kind of amorphous organic polymer as the amorphous organic polymer contained in the thermal transfer recording layers.
Still further, according to a second embodiment of the present invention, there is provided a method of forming an image by means of a thermal head and by making use of a plurality of thermal transfer recording mediums of different colors, each of the thermal transfer recording mediums comprising a substrate and a single-color thermal transfer recording layer formed on the substrate and containing a coloring pigment, an amorphous organic polymer and fine particles, the method comprising a step of successively thermally transferring the single-color thermal transfer recording layers of the thermal transfer recording mediums for each color to an image-receiving member on a basis of image data to thereby form an image based on an area gradation, wherein each of the single-color thermal transfer recording layers which are successively transferred, excluding the single-color thermal transfer recording layer to be transferred latest, is formed to have an average thickness of 0.6 xcexcm or less.
Still further, according to a second embodiment of the present invention, there is provided an image-bearing article comprising; an image carrier; and a transferred multi-color image of dots formed on the image carrier through a successive thermal transferring using the thermal transfer recording medium claimed in claim 11; wherein the dots of the transferred color image excluding the dots of transferred color image positioned highest in the superimposed dots of multi-color which are successively transferred, are formed to have an average thickness of 0.6 xcexcm or less.
Still further, according to a second embodiment of the present invention, there is provided an image-bearing article comprising; an image carrier; and a transferred multi-color image of dots formed on the image carrier from an intermediate image carrier having dots of an intermediate multi-color image transferred through a successive thermal transferring using the aforementioned thermal transfer recording medium; wherein the dots of the transferred color image excluding the dots of transferred color image positioned lowest in the superimposed dots of multi-color which are successively transferred, are formed to have an average thickness of 0.6 xcexcm or less.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.